Manufacture of paper



Reissued Apr. 9, 1935 MANUFACTURE OF PAPER Harold Robert Rafton,Andover,-Mass., assignor to Rafiold Process Corporation, a corporationof Massachusetts No Drawing. Original No. 1,834,903, dated December 1,1931, Serial No. 426,189, February 5,

Application for reissue November 29,

1933, Serial No. 100,350

20 Claims.

This invention relates to the manufacture of paper and more particularlyto paper containing alkaline filler.

The principal object of this invention is to provide a novel method ofusing starch in paper made with alkaline filler.

An important object is to provide a method of using starch which willmeasurably avoid decomposition of the starch in the papermaking process.

A further object is to provide a method of using starch wherein themaximum viscous properties of the starch are retained.

Other objects and advantages of this invention will become apparentduring the course of the following description.

Starch has been used for many years as a constituent. of paper mixes toimpart stiffening, a firmer feel, and the like qualities to paper madetherewith; and where in the claims I use the expression desirablestarch-imparted characteristics ,I refer to qualities such as those justmentioned. I

As I have disclosed in my copending application Serial No. 202,453,filed June 29, 1927, now

Patent No. 1,831,928, issued November 17, 1931,

starch is also particularly valuable in certain cases where alkalinefillers are used in papermaking, for substantially eliminating thefoamforming tendency from otherwise foam-forming mixes. In the abovereferred to application the use of starch in conjunction with alum isalso recommended.

Where starchhas been employed heretofore as a constituent ofxpaper mixesit has been the customary practice to mix it in a compounding and/ortreating device, such as a beater or the like, with an aqueoussuspension of fibrous material and such other material as may beemployed in papermaking such as filler, size, for example rosin size,size precipitant, for example alum, tinting and the like. 'I'his mixusually has a dry solid content of approximately 5%, more or less. Themix after subjection to suifipint treatment in the beater,- is thenordinarily discharged into a container commonly called a beater chest,additional water usually being added. Thereafter the mix may betransferred from the beater chest to a suitable refining engine, usuallya Jordan, at a dry solid content which may be approximately in theneighborhood of 4%. In coinmon practice the mix is at this point usuallydiluted somewhat by the addition of water, and the diluted mix afterjordaning is ordinarily conducted from the Jordan to another containercommonly known as a machine chest. From the machine chest the mix istransferred to a point near the web forming end of a paper machine whereit is largely diluted with water, this point commonly being referred toas the mixing box, water being here added ordinarily in such an amountas to provide a dry content from approximately to 1% or slightly higher,but usually not in excess of I The mix in such highly dilute conditionis then passed through riillers or the like if desired and thereafterthrough screens and-through the headbox of the paper machine on to themachine wire, or into a vat, depending upon whether a Fourdrinier or acylinder machine is employed; and during this passage additional amountsof water are usually added in the form a spray or otherwise.

, This exact procedure is not always followed but in some instances ismodified in accordance with the type of paper being made. For example,in the manufacture of certain types of paper the beating process isalmost if not entirely dispensed with, the ingredients being merelymixed to getherprior to jordaning. In some instances the step ofrefining or jordaning may be partially if not wholly dispensed with.Moreover in some cases the arrangement of steps is different; forexample, the jordaning may take place subsequent to the machine chest,thestock passing directly from the Jordan to the mixing box. Sometimesalso the arrangement of the chests or the number of the chests used isvaried. In general, however, it can be stated that in the papermakingprocess, regardless of the variations which may occur, the ingredientsare normally mixed and/or treated in a relatively concentratedcondition, and maintained therein for a substantial length of time, andthen the mix is subsequently diluted preparatory to delivery to awebforming device and it remains in this dilute condition only arelatively brief period of time.

Under the conditions above outlined which have been customary whenstarch has been previously used in paper mixes, certain disadvantaseshave inhered in its use. is a putrescible material. -It,is subject toattack by molds and the like, and in the course of its passage throughthe beater, chests, and Jordan, up to the point ofdilution, the lengthof time isv such that the starch remains sufiiciently long in the systemfor these deteriorating agencies to act thereon to a considerableextent. .The deterioration seems to be particularly pronounced incertain instances where the system is alkaline as would be the casewhere alkaline filler is employed, particularly where it is added in theFor example starch beater.

The putrescent condition is aggravated if there be present in the mixother putrescible materials such as old paper stock (reworked oldpapers) particularly if such contain reworked coated papers containingcasein. If in addition there be other elements which prolong-thecontinuance of contact of the. starch with the other ingredients of themix such as is customary in modern papermaking equipment, this tendencytoward decomposition is much more manifest. An example of such elementswhich maintain the other ingredients of the mix in contact with thestarch for longer times is where recovery systems are used in the whitewater cycle. Sedimentation systems are common for use on the excesswhite water, and in such instances the recovered stock, which in thiscase would contain starch, is returned to the papermaking operation,commonly to the beater. Another type of recovery system commonly usedand which illustrates the point satisfactorily is the filtration typewhich normally mixes the excess white water from the machine with theso-called sweetener" stock usually taken from the beater or machinechest, and returns the material filtered from the excess white watertogether with the sweetener stock back into one or the other chests.This filtration cycle, as is apparent, returns part'of the starch whichwould ordinarily escape with the white waters back into the papermakingoperation and thus prolongs the contact of the starch with the otherconstituents of the mix and promotes its decomposition.

As a result of the decomposition, not only is the starch in partdeteriorated or destroyed, but

, there is a considerable opinion that such decomposition of .the starchis very injurious inpromoting slime in the paper and also as being incertain cases an agency whichpromote's the formation of soft lumps onthe paper machine, which in turn greatly interfere with production andreduce the quality of the paper made under such conditions.

Another disadvantage inherent in the method heretofore employed in usingstarch is the fact that even though the system were kept entirelysterile so that no growth of molds or micro-organisms could take place,nevertheless the constant v agitation such as is present for example inthe papermaking operation as discussed above, has a tendency to reducethe viscous quality of the starch, which is considered to be .animportant quality of starch for papermaking use. It will be apparenttherefore that the intimate contact of the starch with the otheringredients of the mix, brought about by the agitation it receives inthe. papermaking apparatus, reduces the value of the starch as apapermaking material, and this lessening of the advantageous qualitiesof the starch is more or less proportional to the amount of agitation itreceives.

a I have discovered that the disadvantages inherent in the method ofutilizing starch hitherto employed, can be overcome to a very greatextent by minimizing 'the time and/or intimacy of contact of the starchwith the other constituents of the paper mix and I have devised a methodwhereby my discovery can be practically utilized in the papermakingoperation.

Briefly, I add the starch to the mix at a point late in the paper makingprocess, for example, subsequent to the passage of the mix through themachine chest and preferably at the wet end of the paper machine,whereby the time of contact of the starch with the other constituentsofthe mix is greatly minimized. Moreover the addi tion of the starch inthe dilute stage of the papermaking process acts to decrease greatly theintimacy-of contact of the constituents of the mix and thereby preventsdeterioration of the viscous quality of the starch by diminishing thefrictional action to which the starch is subjected.

Of course, in certain cases such as where the refining engine is placedbetween the final stock chest and the paper machine, the starch may beadded subsequent to the delivery of the stock from this final chest. Inthis case the Jordan acts as an eflicient incorporating means for thestarch with the paper mix, and inasmuch as the time of contact in theconcentrated condition is only very brief, the results are in certaincases wholly satisfactory. However, in most cases I have found itpreferable to efiect the mixing of the starch at the wet end of thepaper machine, usually at the mixing box or at any point which maybe-convenient prior to the delivery of the mix onto the web-formingdevice.

It will thus be apparent that my method of utilizing starch in thepapermaking process avoids to a great extent the deterioratinginfluences formerly inherent in the method of adding starch in thebeater, removes the starch as a source of putresence from the earlierpart of the papermaking operation, tends to prevent in certain cases ina considerable measure the formation of slime and lumps in thepapermaking process, and prevents the'deterioration of the valuableviscous quality of the starch owing to the prevention of prolongedagitation of the starch in contact with the other constituents of themix.

As will be apparent this makes for the more eflicient use of the starchand lesser amounts than formerly were required to give certain desiredproperties to the paper mix or resulting paper can now be used. It isthus apparent that my process is very beneficial from the standpoint ofstarch economy.

In those cases as indicated above where settling 0r filtration cycles onthe excess white waters return the material recovered from the excesswhite water to the earlier stage in the process either in the heaters asis sometimes done with settling systems or to the chests as is sometimesdone with filtration systems it will be apparent that part of the starchin the furnish will be returned to an earlier stage of the process.This, as has been indicated above, is not theoretically the mostadvantageous procedure. However, owing to the fact that the starchoriginally introduced is highly viscous owing to its undeterioratedcondition, as well as to the fact that a. lesser amount of starch may beemployed than formerly, less of the starch than was formerly the casewill tend to be present in the white water coming from the machine andthus only a relatively small quantity will be reintroduced at an earlierstage inthe process. As this quantity is small compared with theoriginal amount of starch employed, and especially if it bereintroduced, as is preferable, in the latter part of the system such asin the machine chest, no serious detriment will be incurred from thepresence of this minor quantity of starch in the system prior to thepassage of the mix from the machine chest. However, if it be feasible,it is especially advantageous in this connec- 'ing operation just priorto or at the dilute stage.

My invention may be conveniently employed in the manufacture either ofsized or substantially unsized papers; Moreover, it may be carried outsatisfactorily in connection with the processes disclosed in various ofmy copending 'applications, that is, the starch may be the only materialadded at the wet end otthe paper ma.- chine, or one or more of thefollowing materials may also be added at this point: alkaline filler,alum, size, precipitated sizing, sodium silicate, precipitated silicate,or the like.

A suitable furnish for use in carrying out my invention is as follows:

Substantially unsizedpaper In the above furnish the'starch is added,preferably continuously, at the wet end of the paper machine. The fillerand/or alum may either be added in the beater with the fibrousconstituents, or at the wet end of the paper machine.

Another suitable furnish is as follows:

Sized paper Pounds Sulphite and soda pulps 1700 Size (e. g. rosin size)45 Alkaline filler (e. g. CaCO:Mg(OI-I)-.-) 300 Size precipitant (e. g.alum) 70 Starchi In the above furnish starch isadded, preferablycontinuously, at the wet end of the paper machine. Preferably at leastpart of the alum should also be added at that point. 'Ihefiller and/orthe size may either be added in the heater, or at the wet end of thepaper'machine.

In both the above furnishes the weights of the size and alkaline fillerrefer to the bone dry basis; the weights of all other constituents referto the air dry basis.

It will be understood of course that the above furnishes are intended asillustrative only and in no sense as restrictive, as widely differingfurnishes give satisfactory results. The starch used may vary widely inamount. Practically speaking, however, although I do not restrict myselfthereto, less than one percent. has but little effect on the finishedpaper and'starch is seldom used in lesser amount in papermaking.

As is well known, starch is customarily employed in the paperma kingprocess by treating raw starch in such a manner as to produce a viscoussolution. This may be suitably accomplished byheating starch and waterto we point where the starch is cooked, i. e., where it becomes asubstantially homogeneous viscous colloidal solution. This solution isthen usually-allowed. to cool. It is in such condition that I preferablyemploy starch in my process. However, starch, i. e., unmodified starch,is not always employed in paperma ng; sometimes the so-called "modifiedstarches are used. A great variety of these with difierent propertiesare on the market, e. g., some are directly soluble in cold water.others give thin boiling solutions.

'of the paper machine.

My process. as will be apparent, is also useful with modified starchesfor although the question of maintaining the viscosity may not be ofsuch great importance with such starches, nevertheless the question ofminimizing the putrescence is of considerable importance, and of coursemy process makes such minimizing feasible.

By the term .alkaline filler I mean substantially water insoluble fillerwhich when agitated in contact with freshly boiled distilled water, sayfor an hour, will impart a pH value to such water greater than 7.0, thatis, which will be on the alkaline side of the neutral point. Amongfillers included in this group may be mentioned calcium carbonate, ofwhich lime mud from the causticizing process is one form; calciumcarbonate magnesium basic carbonate employed in the paper disclosed inmy U. S. Patent No. 1,595,416, dated August 10, 1926; calcium carbonatemagnesium hydroxide disclosed in my U. S. Patent No. 1,415,391, datedMay 9, 1922; and other substantially water insoluble normal or basiccarbonates of alkaline earth metals, (which expression is hereinintended to include magnesium), or compounds, double salts, orphysically associated mixtures of these with one or more other acid soluble materials of a substantially water insoluble nature.

By the term alkaline filler" I also intend to include fibrous materialand/or other material 4 such as paper coatlngconstituents or the likecontaining one or more compounds of the characterreferred to, such asold papers or similar papers, broke", or thalike.

When I use the word paper herein, I use it in the broad sense to includeproducts of manufacture of all types and of all weights and thicknesses,which contain as an essential constituent a considerable amount ofprepared fibre and which are capable of being produced on a Fourdrinier,cylinder, or other forming, felting, shaping or molding machine.

By the term wet end of the paper machine, I intend to include thoseinstrumentalities employed in paper manufacture by which and/ or inwhich a relatively concentrated paper mix is diluted, and treated,conveyed or fed up to the point of web-formation, such as the mixingbox, regulating and proportioning devices, riiliers, troughs, screens,head boxes, inlets, and the like, including also instrumentalities usedin the white water cycle. I

In my copending' application Serial No. 304,167, filed September '5,1928, now Patent No. 1,803,642, issued May 5, 1931, I have disclosed butnot claimed the addition of starch to a fibrous mix at the wet end ofthe paper machine in the manufacture of paper filled with an alkalinefiller.

In my copending application Serial No. 304,175, filed September 5, 1928,now Patent No. 1,803,650,. issued May 5, 1931, I have disclosed andclaimed a method for sizing paper filled with an alkaline filler inwhich size such as rosin size and size precipitant such as alum aremixed in the presence of starch, and the resulting prodhot is added tothe fibrous mix at the wet end Moreover, in my copending applicationSerial No. 319,721, filed November 15, 1928, now Patent No. 1,808,069,issued June 2, 1931, I havedisclosed and claimed a method ofincorporating into paper filled with alkaline filler an inorganic alkalimetal salt -'with a pH value greater than 7.0, for example sodiumsilicate which is precipitable by material which depresses its hydroxylion concentration,

by mixing said alkali metal salt with a precipitant therefor in thepresence of starch, and adding the resulting product to the, fibrous mixat the wet end of the paper machine. I therefore exclude from the scopeof the present speciflcation and claims the addition of starch, in themanufacture of paper filled with alkaline filler,

in this paragraph, together with a precipitant therefor.

While I have described in detail the preferred embodiment of myinvention, it is to be understood that the details of procedure, theproportions of ingredients, and the arrangement of stepsmay be widelyvaried without'departing from the spirit of my invention or the scope ofthe subjoined claims.

31 claim:

1. The method of manufacturing paper filled with alkaline filler,comprislngmixing fibrous material and alkaline filler in the heater, andadding to the resulting mix starch at the wet end of the paper machine.

2. In a method of manufacturing paper filled with alkaline filler thesteps of introducing alkaline filler into the fibrous mix, and of addingstarch to the fibrous mix under conditions favoring the minimizing ofthe time of contact of p the starch with the constituents of the mix.

3. In a method of manufacturing paper filled with alkaline filler thesteps of introducing alkalinefiller into the fibrous mix, and of addingstarch: to the fibrous mix under conditions favoring the minimizingofthe time and intimacy of contact of the starch with the constituentsof the mix. i I

4. In "a method of manufacturing paper filled with alkaline filler thesteps of introducing alkaline filler into the fibrous mix, and of addingstarch to the fibrous mix subsequent to the passage of the mix from themachine chest.

5. In a method ofmanufacturing paper filled with alkaline filler thesteps of introducing alkaline filler into the fibrous mix, and of addingstarch to the fibrous mix atthe wet end of the paper machine.

6. In a method of manufacturing paper filled with alkaline filler thesteps of introducing alkaline filler into the fibrous mix, and of addingstarch and alum to the fibrous mix under conditionsfavoring theminimizing of the time of contact thereof with the constituents of themix.

7. In a method of manufacturing paper filled with alkaline filler theimprovement which comprises adding starch, alum, and alkaline filler toa fibrous mix under conditions favoring the minimizing of the time of,contact thereof with the constituents of the mix, and thereafter makingI paper therefrom.

8. In a method of manufacturing paper filled with alkaline filler theimprovement which comprises adding starch, alum, alkaline filler, and

size to the fibrous mix under conditions favorimizing of the time ofcontact of the the constituents of the mix.

10. ha methodof manufacturing paper filled with alkaline filler thesteps of introducing into starch with the fibrous mix .alkaline fillercomprising calcium carbonate and magnesium compound, and of addingstarch to. the fibrous mix under conditions favoring the minimizing ofthe time of contact of the starch with the constituents of the mix.

11. In a method of manufacturing paper filled with alkaline filler thesteps of introducing into the fibrous mix alkaline filler comprisingcalcium carbonate magnesium hydroxide, and of adding starch tothefibrous mix under conditions favoring the minimizing of the time ofcontact of the starch with the constituents of the mix.

12-. In a method of manufacturing paper filled with alkaline filler thesteps of introducing into the fibrous mix alkaline filler comprisingcalcium carbonate magnesium hydroxide, and of adding starch to thefibrous mix under conditions favoring the minimizing of the time andintimacy of contact of the starch with the constituentsof the mix.

13. In a method of manufacturing paper filled with alkaline filler thesteps of introducing into the fibrous mix alkaline fillercomprisingcalcium carbonate magnesium hydroxide, and of adding starch to thefibrous mix atthe wet end of the paper machine.

14. In a method of manufacturing paper filled with alkaline filler thesteps of adding alkaline 16. The method of minimizing the putrescence ofstarch in the manufacture of paper filled with alkaline fillercomprising adding alkaline filler to the fibrous mix, and withholdingthe addipletely therethrough mix-incorporated starch.

substantially undeteriorated by the alkaline filler.

19. Paper filled with alkaline filler, saidpaper comprising fibrousmaterial, alkaline filler, and aluminum compound resulting from theintroduction of alum into the mix subsequent to the beater, said paperhaving distributed substantially completely therethroughmix-incorporated starch substantially undeteriorated by the alka linefiller. 20. Paper filled with alkaline filler, said paper comprisingfibrous material, calcium carbonate.-

and aluminum compound resulting from the introduction of alum into themix subsequent to the beater, said paper having distributedsubv HAROLDROBERT RAFTON.

